The bis(N-substituted phthalimide)ethers are known intermediates used in the synthesis of certain polyetherimides. These compounds are readily converted to the corresponding bis(phthalic anhydride)ethers, by, for example, hydrolyzing with aqueous sodium hydroxide and neutralizing to form the corresponding tetracarboxylic acid, then treating the tetracarboxylic acid with glacial acetic acid and acetic anhydride to form the dianhydride. These procedures are described in general terms in U.S. Pat. Nos. 3,933,852 and 3,879,428.
The bis(phthalic anhydride)ether is useful as a monomer for the preparation of various polyetherimide homopolymers and copolymers. (See, for example, Kolesnikov, G.S., et al., Vysokomal. Soyed. A9: No. 3, pp. 612-618, 1967.) The dianhydride has been found particularly useful for the preparation of polyetherimide copolymers which are characterized by high heat distortion temperatures and excellent thermal stability, processability and chemical resistance.
Procedures for the synthesis of bis(phthalic anhydride)ethers generally have been complicated, multi-step processes or have been characterized by low yields. For example, Kolesnikov et al. (supra) describe a multistep procedure for making bis(phthalic anhydride)ether from xylene. Other processes have suffered from slow reacton rates and/or undesirable side reactions. Additional steps may be required for removal of impurities which are produced by such side reactions, so that the desired product can be recovered from the reaction mixture in acceptably pure form for subsequent reactions. Procedures for preparing bis(phthalic anhydride)ethers from halo or nitro phthalic anhydride are described in Chemical Abstracts, 94:83799 g (1980) and 95:42680 p (1981). A need remains for a simple efficient synthetic-process for bis(N-substituted phthalimide)ethers, which would result in a savings of time and costs associated with the production of these compounds, and would, in turn, provide an efficient process for production of bis(phthalic anhydride)ether monomers for polyetherimide synthesis, by the reactions generally described above.